1. Field of the Invention
This invention relates in general to the field of polymeric materials containing double bonds which are capable of cross-linking with vinyl or ally lmonomers for the purpose of obtaining, through the use of suitable catalysts, hardened resins suited to many uses.
2. Description of the Prior Art
This technological field in its actual industrial scope extends in practice only to the range of the unsaturated polyesters and their use for the production of a great variety of resins. The notoriety of said unsaturated polyesters, of the hardenable and hardened resins obtained by using the same, and of their industrial uses, makes it unnecessary to give any specific indication as to the very extensive technical and patent literature which relates to them.
However, in the specific field of the unsaturated polymeric compounds and the related resins, it is impossible to admit that for the same an analogy might exist with the field of saturated polymers, in which, besides the polyesters, there exist and are widespread the polyamides which present their own advantageous characteristics, and the polyesteramides which in a first approximation present properties that are intermediate between the polyesters and the polyamides and therefore have specific advantageous applications.
To complete this explanation of the premises of the invention, the fact may also be mentioned that various investigations have been carried out, without satisfactory results, to the end of obtaining unsaturated polyamides that would be more or less truly capable of yielding resins capable of hardening with the intervention of suitable catalysts.
Generally speaking, according to the known technology, such unsaturated polyamides may be obtained by following two methods:
1. -- INTERFACE CONDENSATION BETWEEN BICARBOXYLIC ACID CHLORIDES AND DIAMINES;
2. -- CONDENSATION BETWEEN DIACIDS AND DIAMINES IN THE HEATED STATE WITH ELIMINATION OF WATER.
As to the first method the works of Mortillaro, Russo, Credali and Guidotti of Milano Research Center of Montedison (Italian Pat. Nos. 793,192, 793,191, 793,193 of 1967) and those of Lanzetta, Naglio, Marchetta and Palumbo of the C.N.R. Laboratories of Arco Felice (Naples) (Journal of Polymer Science Vol. II, 913-923 (1973)) are known in particular.
This system, however has the fundamental disadvantage of yielding high molecular weight polymers that are slightly soluble in vinyl and allyl monomers. For this reason, they are not usable for the purpose of obtaining resins that are capable of hardening with suitable catalysts and of being employed for diversified uses analogously to polyester resins.
As to the second method, French Pat. No. 1,578,317 (1970) of Schering Aktiengesellschaft is known in particular. By this method, the condensation reaction is carried out at temperatures around 100.degree. C using maleic anhydride as the unsaturated component. Since at such temperatures the fumerization reaction cannot occur, the resin obtained by the solution of the unsaturated polyamide in vinyl or allyl monomers is not sufficiently reactive with normal peroxidic systems. On the other hand, the synthesis of unsaturated polyamides by direct condensation in the heated state cannot be carried out at temperatures much above 100.degree. C due to the fact that under such conditions the amino groups rapidly attack the maleic or fumaric double bonds (these latter to a lesser degree). Further, the direct condensation of fumaric acid with diamines does not easily occur at the temperatures described in the above patent. This is due among other causes to the insolubility of fumaric acid in the reaction environment.
To sum up, it may thus be stated that the main obstacles to the production and the actual industrial application of unsaturated polyamides are due to the occurrence of the following conditions:
a. -- attack of double bonds by amino groups
b. -- low solubility of the polymers obtained
c. -- low economic efficiency in particular in the case of a synthesis by interface condensation.